Browsing by Subject "Formaldehyde"
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Item Assessing and controlling concentrations of volatile organic compounds in the retail environment(2014-05) Nirlo, Éléna Laure; Corsi, Richard L.; Siegel, Jeffrey A.Retail buildings have potential for both short-term (customer) and long-term (occupational) exposure to indoor pollutants. A multitude of sources of volatile organic compounds (VOCs) are common to the retail environment. Volatile organic compounds can be odorous, irritating or carcinogenic. Through a field investigation and modeling study, this dissertation investigates exposure to, and control of, VOCs in retail buildings. Fourteen U.S. retail stores were tested one to four times each over a period of a year, for a total of twenty-four test visits. Over a hundred parameters were investigated to characterize each of the buildings, including ventilation system parameters, and airborne pollutants both indoors and outdoors. Concentrations of VOCs were simultaneously measured using five different methods: Summa canisters, sorbent tubes, 2,4-dinitrophenylhydrazine (DNPH) tubes, a photoionization detector (PID), and a colorimetric real-time formaldehyde monitor (FMM). The resulting dataset was analyzed to evaluate underlying trends in the concentrations and speciation of VOCs, identify influencing factors, and determine contaminants of concern. A parametric framework based on a time-averaged mass balance was then developed to compare strategies to reduce formaldehyde concentrations in retail stores. Mitigation of exposure to formaldehyde through air cleaning (filtration), emission control (humidity control), and targeted dilution (local ventilation) were assessed. Results of the field study suggested that formaldehyde was the most important contaminant of concern in the retail stores investigated, as all 14 stores exceeded the most conservative health guideline for formaldehyde (OEHHA TWA REL = 7.3 ppb) during at least one sampling event. Formaldehyde monitors were strongly correlated with DNPH tube results. The FMM showed promising characteristics, supporting further consideration as real-time indicators to control ventilation and/or environmental parameters. The vast majority of the remaining VOCs were present at low concentrations, but episodic activities such as cooking and cleaning led to relatively high indoor concentrations for ethanol, acetaldehyde, and terpenoids. Results of the modeling effort demonstrated that local ventilation caused the most uniform improvements to indoor formaldehyde concentrations across building characteristics, but humidity control appeared to have a very limited impact. Filtration used under specific conditions could lead to larger decreases in formaldehyde concentrations than all other strategies investigated, and was the least energy-intensive.Item Assessing sheep’s wool as a filtration material for the removal of formaldehyde in the indoor environment(2014-05) Wang, Jennifer, active 21st century; Corsi, Richard L.Formaldehyde is one of the most prevalent and toxic chemicals found indoors, where we spend ~90% of our lives. Chronic exposure to formaldehyde indoors, therefore, is of particular concern, especially for sensitive populations like children and infants. Unfortunately, no effective filtration control strategy exists for its removal. While research has shown that proteins in sheep's wool bind permanently to formaldehyde, the extent of wool's formaldehyde removal efficiency and effective removal capacity when applied in active filtration settings is unknown. In this research, wool capacity experiments were designed using a plug flow reactor and air cleaner unit to explore the capacity of wool to remove formaldehyde given different active filtration designs. Using the measured wool capacity, filter life and annual costs were modeled in a typical 50 m₃ room for a variety of theoretical filter operation lengths, air exchange rates, and source concentrations. For each case, annual filtration costs were compared to the monetary benefits derived from wool resale and from the reduction in cancer rates for different population types using the DALYs human exposure metric. Wool filtration was observed to drop formaldehyde concentrations between 60-80%, although the effective wool removal capacity was highly dependent on the fluid mechanics of the filtration unit. The air cleaner setup yielded approximately six times greater capacity than the small-scale PFR designed to mimic active filtration (670 [mu]g versus 110 [mu]g HCHO removed per g of wool, respectively). The outcomes of these experiments suggest that kinematic variations resulting from different wool packing densities, air flow rates, and degree of mixing in the units influence the filtration efficiency and effective capacity of wool. The results of the cost--benefit analysis show that for the higher wool capacity conditions, cost-effectiveness is achieved by the majority of room cases when sensitive populations like children and infants are present. However, for the average population scenarios, filtration was rarely worthwhile, showing that adults benefit less from reductions in chronic formaldehyde exposure. These results suggest that implementation of active filtration would be the most beneficial and cost-effective in settings like schools, nurseries, and hospitals that have a high percentage of sensitive populations.Item Exposure to hazardous air pollutants in homes(2010-05) Hun, Diana Esther; Corsi, Richard L.; Siegel, Jeffrey A.; Morandi, Maria T.; Novoselac, Atila; Paterson, Robert G.Prior studies have found that human exposure to hazardous air pollutants (HAPs) occurs in homes; however, the depth of these assessments was limited by the extent of the analyzed data. The present Ph.D. dissertation focused on air contaminants of concern in residential buildings, the possible sources of these pollutants, and population subgroups with greater contaminant risk. This research also evaluated the effects of building characteristics and household activity patterns on indoor pollution and risk levels. To this end, an in-depth analysis was performed of data from the Relationships of Indoor, Outdoor and Personal Air (RIOPA) study, one of the most comprehensive exposure assessments to date. Using personal concentrations from the RIOPA study, a cancer risk assessment was performed to identify both important pollutants and populations at higher risk. The analyzed compounds were acetaldehyde, benzene, chloroform, carbon tetrachloride, p-dichlorobenzene (p-DCB), ethylbenzene, formaldehyde, methylene chloride, methyl tert-butyl ether (MTBE), styrene, trichloroethylene and tetrachloroethylene. Results indicate that Hispanics and non-Hispanic whites had median cumulative cancer risks (CCR) of 520×10-6 and 440×10-6, respectively, for which the main contributors were formaldehyde, p-DCB, acetaldehyde, chloroform and benzene. Statistically significant differences in CCR between and within Hispanic and whites were primarily due to exposures to p-DCB. Exposure to formaldehyde was further investigated because this compound was the largest contributor to CCR for 69% of Hispanics and 88% of whites, and because most participants had similar cancer risks from these exposures (median = 260×10-6, coefficient of variance = 28%). Results suggest that the U.S. population may be experiencing chronic exposures because of long-term formaldehyde emissions from pressed-wood materials bound with urea-formaldehyde resins. Source removal may be the most effective way to decrease these chronic exposures. Benzene was also examined further because it is a known human carcinogen. Results show that indoor benzene concentrations increased as the proximity of parked vehicles decreased. Residing in a home with an attached garage could lead to exposures to benzene ten times higher than while commuting in a car in heavy traffic, and with mean excess cancers of 17×10-6. Detached garages could reduce health risks from exposure to benzene and other gasoline-related pollutants.Item Formaldehyde yields from methanol electrochemical oxidation on platinum and supported catalysts(Texas Tech University, 1999-12) Childers, Christina L.The formation of formaldehyde during methanol electrochemical oxidation is being measured with a fluorescence assay in order to assess the importance of formaldehyde as a reaction intermediate and source of efficiency loss in direct methanol fuel cells. Initial studies have focused on the oxidation of methanol on polycrystalline platinum. The formaldehyde yields approached 30% of the total electrolysis charge at 0.2-0.3 V (vs. a KCI saturated Ag/AgCI reference electrode) for methanol concentrations between 15 mM and 0.3 M in 0.1 M perchloric acid. The formaldehyde yields were lower at more positive potentials, as other oxidation pathways became dominant. However, the rate of formaldehyde production increased up to 0.5 V. These initial studies have demonstrated that formaldehyde, which is often not detectable with modern in situ spectroelectrochemical analysis techniques, can be produced in significant amounts during methanol electrochemical oxidation. More recent work has focused on the formation of formaldehyde during methanol electrochemical oxidation on supported platinum and platinumruthenium catalysts. Solid, polycrystalline platinum-ruthenium alloys have been considered. Other catalysts studied have been suspended in Nafion and supported on glassy carbon. Methanol oxidation on the catalysts has resulted in low formaldehyde yields, below 2% at all potentials studied. The low formaldehyde yields, which result from more complete methanol oxidation, are believed to arise from the ability of partial oxidation products to be transported to an array of active catalyst sites dispersed within the three dimensional Nafion film network. Efforts to eliminate these volume effects through techniques such as electrochemical depositions of catalyst crystallites by reduction of transition metal salts onto solid, glassy carbon electrodes; direct metal nanoparticle deposition onto solid, glassy carbon electrodes using a hydrogen tube furnace; and "sticky" carbon methods for metal/wax/carbon type electrodes have been under investigation.Item Methanol electrochemical conversion to formaldehyde over bulk metal and supported catalysts(Texas Tech University, 2006-05) Islam, Mohsina; Korzeniewski, Carol; Casadonte Jr., Dominick J.; Liu, ShaorongThe electrochemical oxidation of 1.0 M CH3OH in 0.1 M H2SO4 over different types of platinum-ruthenium (PtRu) materials was investigated. Focus was on the determination of formaldehyde (H2CO) produced as a function of Ru content in arc-melted bulk alloys and nanometer-scale catalyst materials. A sensitive fluorescence assay for formaldehyde, which had a detection limit down to 100 nM H2CO, was employed. The reaction potentials, reported in volts versus the reversible hydrogen electrode reference (VRHE), were in the range of 0.5 VRHE to 0.8 VRHE. The lower potentials approach voltages that have technological relevance to fuel cells. Electrolysis was performed on 50 ƒÝL samples for a period of 180 s. Based on the coulometry, the reactant depletion in the cell is below 1%. In experiments with bulk PtRu alloys, three samples with respective Ru mole fraction (XRu) of 0.1, 0.3 and 0.9 were employed. Reactions were also carried out on bulk polycrystalline Pt for reference. Compared to Pt, the H2CO yields were lower for the oxidation of methanol over PtRu. Among the PtRu alloys, the H2CO yields decreased with increasing XRu, except at the lowest potential studied (0.5 VRHE), where the formaldehyde yield was lowest for the sample with XRu = 0.3. The finding is consistent with XRu = 0.3 being the most active PtRu composition for methanol electrochemical oxidation at ambient temperature. The results are attributed to lower reactivity of methanol on the electrode with XRu = 0.9 at 0.5 VRHE due to due to blocking of initial dissociative chemisorption steps by inhibiting oxides present at Ru sites. Compared to bulk electrodes, methanol oxidation over nanometer-scale catalyst resulted in H2CO yields below 10 % under the conditions studied. The following catalyst materials were used on gold electrode: Pt-Black, C/Pt, 10 wt % on Vulcan XC-72R carbon, PtRu black with XRu = 0.5, PtRu catalyst prepared via a sonochemical (SC) method with XRu = 0.1, 0.25 and 0.5. High current densities were achieved during sample electrolysis. The results indicate the nanometer-scale catalyst converts methanol to more complete oxidation products. The findings are consistent with earlier studies and are attributed to readsorption and complete oxidation of H2CO within multiple catalyst layers, leading to lower H2CO yields. Similar to results for smooth, bulk electrodes, the H2CO yield was significantly higher for methanol oxidation over the lowest Ru content nanometer-scale catalyst (XRu= 0.1) and approached the response for Pt black. This project also advanced the design of the small volume electrolysis cell employed for the thesis research by incorporating a machinable MACOR glass ceramic disk window, which resists oxygen permeation. The cell response was characterized by observing the reversible, diffusion controlled waves for hexamine ruthenium trichloride (Ru (NH3)6Cl3) in cyclic voltammetry measurements.Item Methanol electrochemical conversion to formaldehyde over bulk metal and supported catalysts(2006-05) Islam, Mohsina; Korzeniewski, Carol; Liu, Shaorong; Casadonte Jr., Dominick J.The electrochemical oxidation of 1.0 M CH3OH in 0.1 M H2SO4 over different types of platinum-ruthenium (PtRu) materials was investigated. Focus was on the determination of formaldehyde (H2CO) produced as a function of Ru content in arc-melted bulk alloys and nanometer-scale catalyst materials. A sensitive fluorescence assay for formaldehyde, which had a detection limit down to 100 nM H2CO, was employed. The reaction potentials, reported in volts versus the reversible hydrogen electrode reference (VRHE), were in the range of 0.5 VRHE to 0.8 VRHE. The lower potentials approach voltages that have technological relevance to fuel cells. Electrolysis was performed on 50 ƒÝL samples for a period of 180 s. Based on the coulometry, the reactant depletion in the cell is below 1%. In experiments with bulk PtRu alloys, three samples with respective Ru mole fraction (XRu) of 0.1, 0.3 and 0.9 were employed. Reactions were also carried out on bulk polycrystalline Pt for reference. Compared to Pt, the H2CO yields were lower for the oxidation of methanol over PtRu. Among the PtRu alloys, the H2CO yields decreased with increasing XRu, except at the lowest potential studied (0.5 VRHE), where the formaldehyde yield was lowest for the sample with XRu = 0.3. The finding is consistent with XRu = 0.3 being the most active PtRu composition for methanol electrochemical oxidation at ambient temperature. The results are attributed to lower reactivity of methanol on the electrode with XRu = 0.9 at 0.5 VRHE due to due to blocking of initial dissociative chemisorption steps by inhibiting oxides present at Ru sites. Compared to bulk electrodes, methanol oxidation over nanometer-scale catalyst resulted in H2CO yields below 10 % under the conditions studied. The following catalyst materials were used on gold electrode: Pt-Black, C/Pt, 10 wt % on Vulcan XC-72R carbon, PtRu black with XRu = 0.5, PtRu catalyst prepared via a sonochemical (SC) method with XRu = 0.1, 0.25 and 0.5. High current densities were achieved during sample electrolysis. The results indicate the nanometer-scale catalyst converts methanol to more complete oxidation products. The findings are consistent with earlier studies and are attributed to readsorption and complete oxidation of H2CO within multiple catalyst layers, leading to lower H2CO yields. Similar to results for smooth, bulk electrodes, the H2CO yield was significantly higher for methanol oxidation over the lowest Ru content nanometer-scale catalyst (XRu= 0.1) and approached the response for Pt black. This project also advanced the design of the small volume electrolysis cell employed for the thesis research by incorporating a machinable MACOR glass ceramic disk window, which resists oxygen permeation. The cell response was characterized by observing the reversible, diffusion controlled waves for hexamine ruthenium trichloride (Ru (NH3)6Cl3) in cyclic voltammetry measurements.Item Removal of formaldehyde from indoor air : enhancing surface-mediated reactions on activated carbon(2013-08) Carter, Ellison Milne; Katz, Lynn E.; Speitel, Gerald E.Formaldehyde is a ubiquitous and hazardous indoor air pollutant and reducing concentrations in indoor environments is a public health priority. The goals of this doctoral work were to advance analytical methods for continuous monitoring of formaldehyde at very low concentrations (sub-20 ppb[subscript v]) and to improve fundamental, mechanistic understanding of how structural and chemical properties of activated carbon influence removal of formaldehyde from indoor environments. To achieve these goals, emerging sensor-based technology was evaluated for its ability to detect and quantify ppb[subscript v]-level formaldehyde concentrations on a continuous basis at relative humidity levels characteristic of residential indoor environments. Also, a combination of spectroscopic and selective titration techniques was employed to characterize molecular-level structural and chemical properties of traditional and chemically treated granular activated carbon (GAC). In addition to selecting two different commercially available GACs for study, design and preparation of a laboratory-prepared, chemically treated GAC was pursued to create nitrogen-doped GAC with desirable surface chemical properties. Performance of all GACs was evaluated with respect to formaldehyde removal through a series of packed bed column studies. With respect to continuous formaldehyde monitoring, a method detection limit for emerging sensor technology was determined to be approximately 2 ppb[subscript v], and for relative humidity levels characteristic of indoor environments (> 40%), quantitative, continuous formaldehyde measurements less than 10 ppb[subscript v] were robust. The two commercially available GACs tested were both capable of removing formaldehyde; however, the GAC with greater density of basic surface functional groups and greater electron-donating potential (Centaur) removed twice as much formaldehyde (on a GAC mass basis) as the less basic GAC (BPL). A laboratory-prepared GAC (BPL-N) was successfully created to contain pyridinic and pyrrolic nitrogen, which was associated with increased surface density of basic functional groups, as well as with increased electron-donating potential. BPL-N exhibited better removal capacity for formaldehyde than BPL and Centaur. Furthermore, packed bed column studies of BPL-N and BPL formaldehyde removal performance yielded evidence to support the hypothesis that electron-donating potential, especially nitrogen functional groups at the BPL-N surface, promote catalytic removal of gas-phase formaldehyde via oxidation.